Parking meters in general permit vehicles to be parked along a street for an allowable period of time, which is determined by the amount of money inserted therein. A mechanical clockwork or electronic timer inside the parking meter runs down the allowable time until it reaches zero time, and causes an overdue parking indication to appear through a window of that meter. In recent years, parking meters have been improved greatly by the development of low powered electronic circuitry, ultrasonic transmitters and receivers, and wireless communication systems.
Revenues from parking meters are normally used by municipalities to cover the ever-increasing costs of maintaining its infrastructure in a good condition. Therefore the improved modern meters are attractive for a municipality for increasing the revenues generated from its metered parking systems.
A first example of modem parking meters is disclosed in U.S. Pat. No. 5,454,461 issued on Oct. 3, 1995 to James P. Jacobs. The electronic parking meter described therein includes; means for detecting and determining the denomination of coins, a liquid crystal display having a digital tie counter, a sonar transducer for detecting the presence of vehicles, and an infrared transceiver enabling parking authority personnel to communicate with the meter. The meter is operated in three conditions including an off condition, an inactive condition and an active condition to provide conservation of power so that the meter is entirely battery operated.
Electronic parking meters having these described features are especially attractive to municipalities because all time expiry conditions thereof are readily communicated to parking authority personnel via a central computer. The parking authority personnel may thereby be effectively dispatched to those vehicles in violation of parking rules, to issue parking tickets to the owners of those vehicles. Such improvement of a metered parking system is known to increase revenues from those meters considerably.
Other examples of modern electronic parking meters are solar powered and also have liquid crystal displays, for displaying advertisement messages to users of metered parking spaces. These particular meters are disclosed in U.S. Pat. No. 5,442,348, issued on Aug. 15, 1995 to Joshua Mushell, and in U.S. Pat. No. 4,872,149 issued on Oct. 3, 1989 to Gary W. Speas. Hence, another source of income for a municipality having electronic parking meters is generated from the sale of advertising messages displayed on the liquid crystal displays of the meters, to businesses located near the metered parking spaces.
The replacement of a quantity of conventional mechanical meters with newer electronic models represents, nonetheless, a substantial investment of funds for the purchase of the electronic units, an investment of manpower time and wages for replacing the conventional meters by the electronic models, and a financial loss in the writing-off of the undepreciated value of the conventional meters. Therefore, in a period of budget restraint as during the present times, the acquisition of electronic meters is not economically feasible for many municipalities.
As an alternative to an entire replacement of conventional parking meters by electronic units, a number of retrofit electronic devices exists to enhance the operation of conventional parking meters. Such a unit mounts adjacent to a conventional parking meter, and connects to the clockwork of the meter. A first and second examples of these controllers are described in U.S. Pat. No. 3,535,870 issued on Oct. 27, 1970 to Harold B. Mitchell, and in U.S. Pat. No. 3,999,372, issued on Dec. 28, 1976 to Welch et al.
The controller of the first example or the control unit of the second example, comprises an ultrasonic transmitter and a receiver to detect the presence of a vehicle near a standard parking meter. Once the vehicle leaves the parking space, the meter is automatically returned to zero time such that a next vehicle cannot take advantage of the remaining time credit of the meter. In the first case, the controller is connected inside the meter to a mechanical switch, and has a solenoid for resetting the clock hand to a zero time position. Similarly, in the latter example, the control unit is connected to a pair of solenoids and a pair of mechanical switches mounted inside the meter head.
The installation of the retrofit units of the prior art requires intensive modifications to the clockwork of conventional parking meters. These modifications are usually better done by the original manufacturer of the meters. Therefore, the upgrading of a quantity of conventional meters with the retrofit units represents also a substantial investment in manpower time and wages to remove and send the meters to the manufacturer, and to reinstall the modified meters. Other expenses include the cost for modifying the clockwork, and the lost of revenue from the parking system when substitutable meters are not available to replace those meters removed for alteration.